Stator for electric machines

ABSTRACT

A stator for electric motors including a rotor and consisting of at least a pair of stacks each comprised of a plurality of laminations arranged with their sides in the direction of the rotor axis, the edge portions of the laminations running in the axial direction being bent inwardly towards the stator bore and maintained in spaced-apart relation at a position predetermined with regard to the magnetic flux lines and being permanently fixed in this position solely by means of a moulded compound, each lamination stack consisting of undivided laminations comprising a north and a south pole, each main pole consisting of the lamination edges of two adjacent lamination stacks.

The present invention relates to a stator for electric machines,especially machines of the kind constructed with separately wound polesand with yoke components required between these poles for the magneticflux. The invention also comprises a method for the production of thestator in question.

A large number of motor variants, e.g. commutator motors and shaded polemotors, are provided with stators as specified above. These motors aregenerally designed for high speeds, have small or medium ratings, andare used for, for instance, fans, blowers, vacuum cleaners and similarappliances. However, these motors have certain serious disadvantages.Their dimensions are large and they are heavy. This is partly on accountof the collector system required for certain types of motor but it isalso because of the solid and cumbersome pair of poles. The stators havemechanically weak sectors which impede the accurate centering of therotor system and entail considerable air gap requirements with resultantpoor efficiency. The very poor efficiency produces great thermal losseswhich directly preclude the construction of larger units. The overallpicture is of windings that are very compact, surrounded to a very greatextent by large masses of sheet metal and consequently have smallsurfaces for thermal radiation. The stators of these motors are made oflaminations stacked at an angle of 90° to the longitudinal axis of therotor. The lamination sections are of a complex nature and this incurs agreat deal of material wastage and expensive joining of the laminations.

A typical example of this technique is the two-pole commutator motorillustrated in FIG. 1, which shows an end view and a partial sectionthrough the motor, the two salient poles 1 and 2 of which are conjoinedby the yoke components 3 and 4. The two poles are encircled by thewindings 5 and 6 respectively. The current through the windingsgenerates a magnetic flux 7, which passes from pole 1 through the rotor8 to pole 2. The magnetic circuit is closed by the return flux in thetwo yoke components 3 and 4. The sectional areas of these yokecomponents are accordingly dimensioned to allow the passage of the totalflux. A certain pole width, indicated by the numeral 9, is required torun the motor. This width gives the pole a sectional area which is manytimes that of the yoke components 3 and 4. Consequently the flux densityin the poles will be considerably lower than in the yoke components, andcertain parts of the salient poles, for instance that indicated by thenumeral 10, have slight or zero magnetic flux. The motors as describedabove always have proportionally very considerable core losses. Inaddition there is very little possibility of cooling as the windings arealmost completely encircled by the masses of iron, yokes and poles.This, together with the core losses, presents serious problems withregard to the cooling of motors of this type.

In order to overcome these deficiences proposals (U.S. Pat. Nos.2,449,021 and 3,591,819) have previously been made for arranging thestator laminations in the logitudinal direction of the rotor and bendingthe edges of the laminations in towards the stator bore. Since themagnetic flux into the stator bore will then be entirely determined bythe relative positions of the laminations edges, serious problems havebeen encountered instead in aligning these edges. One way of solvingthese problems has been to bend the extreme outer part of the edge toform a 90° angle with the laminations and accordingly let the outer endsof the laminations abut each other. Another solution has been to securespecial fixtures to the edges of the laminations in order to determinetheir relative positions. Both these proposes solutions produce aninaccurate circular-shaped stator bore and it has not proved possible tomachine this bore by turning or other similar methods. Apart from theinaccuracy of form of the stator bore the production of these devices isexpensive as well. One way to reduce the costs has been to divide thelaminations and produce stacks that can be slid into each other. Such anarrangement, however, produces heavy losses as the magnetic flux has topass an air gap.

SUMMARY OF THE INVENTION

It has, however, according to the present invention been possible toeliminate the above mentioned drawbacks by producing an electric motorhaving a stator which is characterized thereby that the laminations ofthe stator are arranged as a stack having its sides in the axialdirection of the stator, the edge portions of the laminations running inthe axial direction being bent towards the stator bore and maintained inspaced apart relation at a position predetermined with regard to themagnetic flux lines by the aid of a moulded compound, each laminationstack consisting of undivided laminations being arranged to encircle anorth pole and a south pole.

The stator according to the invention can be designed in such a way thatthe stator windings are arranged either around the edge portions oflaminations adjacent to the stator bore or around the yoke components ofthe laminations.

A very large advantage is obtained if in the latter case the windingsare substantially free from mould compound and an open air gap is formedbetween the yoke components of the stator and the rotor. It is therebypossible to obtain a very efficient cooling for the stator windings.These will have a free radiation surface both outwards and inwards, atthe same time as cooling by natural or forced convection can be used.The possibility of increasing the cooling capacity of the stator bythese large cooling surfaces will on the whole contribute towards acooler motor, which in turn improves the efficiency and the poweroutput. The windings can easily be applied mechanically.

The motor will have considerably smaller dimensions as compared to acorresponding, conventionally built motor, as the pole according to thepresent invention will have the same sectional area for the magneticflux as the yoke components and all superfluous masses or iron therebycan be eliminated. The masses of copper may also be considerably reducedright down to one third as compared to conventional motors having anequal power output.

The lamination wastage can be reduced nearly to nil as the laminationscan be manufactured as rectangles or parallelograms and the productioncosts are thereby correspondingly reduced. The laminations may also begiven non-uniform thickness for adjusting the flux resistance.

It is easy to arrange additional insertions of induction rings, socalled shaded poles by utilizing the space between the separatelaminations for insertion of laminations having short circuited currentcurcuits. The unevenly bent laminations may get different length butthis can as mentioned hereabove resourcefully and easily be compensatedwith varying lamination thickness in order to reach a uniform fluxresistance.

As the laminations are made without any lamination wastage it isadvantageous to use sheet metal qualities having an "aligned" magneticflux character, without appreciably influencing the total costs.

A thermosetting resin or the like can be used as the mould compound. Forobtaining a good dispersion of the magnetic flux the compound may bemagnetic conductive.

The stators according to the invention are manufactured thus that thepreviously bent laminations with windings are inserted into a mould,whereupon an internal centre mandrel is inserted and a mould compoundfinally is introduced into the cavity and brought to set.

By arranging the laminations edges adjacent to the stator bore todelimit a cavity having a diameter smaller than the mandrel prior to theinsertion of this, it is obtained that the laminations edges are pressedoutwards and abut the mandrel when this is inserted into the cavity.

By means of this flexible self-adjustment against the center mouldmandrel, eventually in combination with electric orientation oflamination distance etc., it is obtained a stator having extremelynarrow tolerances for the stator bore. The air gap geometry betweenrotor and stator is thereby improved thus that smaller air gaps can beaccepted for the motors, which heavily will improve the efficiency andoutput.

The envelope surface of the mandrel may be provided with grooves orridges for guiding the laminations edges.

If the windings are arranged around the yoke components of thelaminations it is essential that the mandrel is pressed against theseduring the pouring in order not to allow the mould compound to enterinto the windings.

BRIEF DESCRIPTION OF THE FIGURES

The invention will herebelow be further described with reference to theaccompanying drawings;

FIG. 2 of which show an end view and a cross-sectional view of a motoraccording to the invention;

FIG. 3 shows a partial section of stator portion together with mouldingtool;

FIGS. 4 and 5 show a partial section of the laminations embedded inplastics and abutting the center mandrel;

FIG. 6 is a similar view showing another embodiment of the invention;

FIGS. 7 and 8 show a partial section through a stator designed withespecial magnetic flux relations;

FIG. 9 shows a detail of a stator lamina with magnetic flux arrows;

FIGS. 10a and 10b show the design of the laminations edges adjacent thestator bore;

FIG. 11 is a partial end view and section of an especial windingarrangement, and;

FIG. 12a and 12b show a perspective view of a motor according to theinvention compared to a conventional motor having equal performancecharacteristics.

DESCRIPTION OF SPECIFIC EMBODIMENTS

In FIG. 2 the salient poles marked with brackets 11 and 12 are connectedby yoke components 13 and 14 so that a closed magnetic flux is generatedwhen coils 15 and 16 are fed with a current. The yoke components areformed by a number of thin laminations 17 which are pressed against eachother, the interengaging surfaces of which are oriented in the axialplane of the motor. The yoke components 13 and 14 continue in the poleportions 11 and 12 by means of an unbroken extension of the laminations17, at the same time as these are aligned and spaced apart from eachother in order to follow the imagined and ideal flux curve 18-24 whichcontinues into the salient pole 11. The space 25 between the laminationsthus formed as a flux curve, is filled with a plastics compound, bywhich the laminations are secured in reciprocal relation and which givessuch a width to the salient pole 11 that the best possible magnetic fluxdispersion 26 is obtained for the rotor 27.

FIG. 3 shows a partial section through a yoke component 30, a poleportion 31, a winding 32 and a plastics moulding tool comprising anouter mould 33 and a center mandrel 34. The yoke component 30 consistsof seven laminations 35. These laminations are bent in such a mannerthat they follow imagined ideal magnetic flux lines which like a fanruns into and through the salient pole 31. When the stack of laminationsand the winding 32 has been placed into the outer mould, the laminationsedges 36 will have a position delimited by a circular cylinder having asomewhat smaller diameter D₁ than the desired stator bore diameter D₂.By inserting the center mandrel 34, the diameter of which is D₂, the endsurfaces 36 of the laminations are pushed outwards to diameter D₂ wherethey will be secured in desired interrelation by aid of plastics mouldcompound 37. This flexing outwards of the thin laminations willguarantee a metallic contact to D₂ whereby a very good tolerance can beobtained in the stator bore.

One demand which must be put on an electric motor is that the air gapbetween stator and rotor must be constant. This air gap is determined bythe accuracy of the rotor and stator surfaces facing each other and bythe fitting of the rotor in the hearing. A conventional rotor is easy tomachine by turning or the like and it can be given a very accuratecylindric surface. The stator bore according to the invention and otherproposed embodiments with the laminations edges facing the stator boreare, however, difficult to machine. A turning tool would, for instance,stamp at the laminations edges and would very soon be worn out due tofillers such as silica or glass in the plastics compound according tothe present invention. The shape of the stator makes it furthermoredifficult to chuck up in a lathe and the operation should becomeextremely expensive.

Another demand which has to be fulfilled by a stator according to theinvention is that the direction of the magnetic flux is not altered, andfor this reason it is necessary to obtain a good binding between thelaminations and the plastics. The distance between the separatelaminations must be secured with no other aid than the plastics and itis also necessary to obtain a sinusoidal flux dispersion if that isdesired.

All these demands are solved according to the invention in the mannerstated hereabove and as further described in connection to FIGS. 4 and5. The laminations 40 are here shown embedded in the plastics 41 and thelaminations edges 42 which are pressed outwards by the aid of a centermandrel define in cross-section a perfect circle. The plastics used hasa tendency of shrinking and a wavy-formed line 43 appears between thelaminations 40. A desired larger air gap is thereby obtained and at thesame time it is secured that the plastics when the motor is gettingwarmer will not bulge out from the laminations edges.

FIG. 5 shows a further manner to guide the lamination 51. The centermandrel may be provided with grooves 52 against which the laminationsedges are pressed. It is also in this case, which is shown in section,obtained a perfect circle. The moulded plastics is further distancedfrom the lamination edges.

Machining of the stator bore is in practice impossible which can clearlybe seen from FIGS. 4 and 5, but by means of the method according to theinvention is every kind of machining unnecessary as the laminationsedges give the desired perfect periphery. Instead of providing themandrel with grooves as shown in FIG. 5 it is possible to arrange ridgeson an otherwise smooth mandrel and let the laminations edges pressagainst these.

FIG. 6 shows the manufacture of a stator where the windings have beenarranged around the yoke components. The mandrel 61 will in this casepress against the windings 62 and as the laminations 66 are bentoutwards at the edges 67 there will be a tension in the yoke component63, which tension further will press the windings against the mandrel.By this arrangement penetration of liquid mould compound 68 from thebore 64 into the windings is made difficult or even impossible. It isalso possible to arrange some blocking device at the winding sidesturned towards the bore. In this manner it is obtained free windingswhich can be cooled very effectively as well on the outside as on theside turned towards the rotor. A comparatively large free air space isgenerated between the rotor and the windings. This advantage is of mostessential importance for the motor efficiency.

FIG. 7 shows in a partial section an yoke component 70 with a salientpole 71, which is encircled by the winding 72. The yoke component 70 isstacked from laminations 73 in the same manner as described inconnection to FIG. 3, but the laminations are in the salient poleoriented in such a manner that a larger flux density is obtained at theouter flank 74 of the salient pole, whereas a lower flux density isobtained at the central portion 75 of the pole. If a concentratedmagnetic flux for any reason is wanted in the central portion salientpole it is possible to arrange the lamination such as shown by the dashoutline 76.

A simple way to adjust the magnetic flux is as mentioned hereabove toalter the thickness 77 of the laminations. A continuous reduction of thelamination thickness 77 from the center of the pole out towards theflanks can, for instance, compensate the fact that the centrallaminations are longer than the flank laminations.

The edges of the laminations, which follow the stator bore can also begiven a gentle spiral form thereby that they are angle-sheared or theycan be split open and formed aiming at a variation of the magnetic flux.

FIG. 8 shows a partial section of a motor type generally referred to asa "shaded pole motor". The figure shows an yoke component 80 with asalient pole 81, both of which are formed by laminations 82 stacked inthe manner described in connection to FIGS. 2-4. An induction coil 83has been fitted between the flank laminations 84 and 85 of the salientpole 81 in order to give the motor a certain starting torque. A closedsmaller magnetic flux 87 is obtained in the particular bent lamination88 where the main magnetic flux 86 passes through the induction coil 83.

FIG. 9 shows in a greatly enlarged view an embedded lamination 90.Before the moulding mandrel were inserted into the mould die thelamination 91 take up the position against diameter D₁. After thepouring of the mould compound follows the lamination diameter D₂. Thetolerance on this measure can be made extremely narrow in order to makethe air gap q₁ between rotor D₃ and stator D₂ electrically optimal. Theair gap losses can hereby be maintained small as compared to the commonlosses at conventional motors of this type. The size of air gap q₂ isshown in the figure for comparison in the same scale. The magnetic fluxis marked with numeral 92 on FIG. 9. It is obtained a tangentialdispersion of the magnetic flux if the lamination 90 is split open andis bent up to any stepped form.

FIGS. 10a and 10b show how the edges of the laminations are arranged asseen from the stator bore. In FIG. 10a the edges 101 of the laminations101a are straight but they are given a spiral form. The edges 101 areembedded in the mould compound 102. In order to obtain a dispersion ofthe magnetic flux the edges 105 of the laminators 107, as shown in FIG.10b, have been split open and bent outwards whereby stepped formations103 are formed in the edges 107 the edges.

FIG. 11 shows a partial end view and section of another motor embodimentcomparable to FIG. 2. The motor according to FIG. 2 has its salientpoles encircled by two current coils. These coils have according to theembodiment shown in FIG. 11 been replaced by coils 110 and 111 which arearranged to encircle the yoke components 112 and 113 of the motor. Thisarrangement gives very large advantages as the same number ofampere-turns as in FIG. 2 in this embodiment will get a heavilyincreased radiation volume. The coils are thin and have large coolingsurfaces 114 and 115 as well out towards the surroundings as inwardsagainst the air stream generated by the rotor. The windings heads of thecurrent coils can be kept at minimum and the motor will thereby getsmaller overall measures. This arrangement is possible as the magneticflux generated by the coil already inside the coil is divided on thelaminations 116, which thereupon directly and independent of each otherlead the flux to the portion of the salient pole where the laminationfollows the stator bore.

FIGS. 12a and 12b show in simple perspective views on one hand aconventional motor 121 and on the other hand a motor 122 for the samepower output but constructed in accordance with the embodiment shown inFIG. 11. These figures show clearly the dimensional gains.

What is claimed is:
 1. A stator for electric motors including a rotorand consisting of at least a pair of stacks each comprised of aplurality of laminations forming a yoke component in the axial plane ofthe motor and having pole portions extending from opposite sides of theyoke component arranged with their sides in the direction of the rotoraxis, windings surrounding the yoke components, means defining an openair gap between the yoke components and the rotor, the terminal portionsof the laminations running in the axial direction being bent inwardlytowards a stator bore and the outer edges thereof maintained inspaced-apart relation at positions predetermined with regard to themagnetic flux lines and being permanently fixed in this position solelyby means of a moulded compound, said edge portions facing the statorbore and being disposed on the periphery of a circular cylinder definingthe stator bore, each lamination stack consisting of undividedlaminations comprising a north and a south pole, each main poleconsisting of the lamination edges of two adjacent lamination stacks. 2.A stator as claimed in claim 1 wherein the moulded compound defines awavy-formed line between the outer edges of the laminations therebyproviding an air gap.
 3. A stator according to claim 1, characterizedthereby, that the moulded compound is magnetically conductive.
 4. Astator according to claim 1, characterized thereby, that the windingsare mainly free from the moulded compound.
 5. A stator according toclaim 1, characterized thereby, that the stator laminations are made ofvarying thickness.
 6. A stator according to claim 1, characterizedthereby, that laminations edges adjacent to the stator bore are arrangedin spiral form.
 7. A stator according to claim 1, characterized thereby,that the laminations edges adjacent to the stator bore are stepped.